3-Phase BLDC Drive Using Variable DC Link Six
Contents
1. FAULT 0 GPIO PA6 Protection Logic RESET GPIO PA7 Buton GPIO PB BO B1 B3 amp Switch UNI 3 B6 expansion User LED connector B4 B5 B6 Encoder Inter face 3 3V Analog Power Supply SI VEDA ADC B4 Tacho Generator IE a Interface 3 3V Digital re gt VDD IO Power Supply lt gt RS 232 Interface EEPROM 5V Power Interface Supply 12V Power GPIO PB SPI SCI Supply HEADER HEADER HEADER Figure 4 2 Block Diagram of the MC56F8013 Controller Board 4 3 3 Phase Power Stage with DC DC Inverter Lite Freescale Semiconductor s embedded motion control series 3 Phase Power Stage with DC DC Inverter Lite is a 12V 42V 10A surface mount power stage In combination with one of the embedded motion control series control boards it provides a software development platform allowing algorithms to be written and tested without the need to design and build a power stage It supports algorithms that use Hall sensors and encoder and back EMF electromotive force signals for sensorless control The 3 Phase Power Stage with DC DC Inverter Lite does not have any overcurrent protection independent of the control board therefore care in its setup and use is required if a lower impedance motor is used Current measuring circuitry is set up for2. 1 Freescale Semiconductor 15 Control Theory 2 4 Speed and Voltage Control Commutation ensures proper rotor rotation of the BLDC motor while the motor speed depends only on the amplitude of the applied voltage The amplitude ofthe applied voltage is adjusted by the variable DC link six step inverter using pulse width modulation The required speed is controlled by a speed controller The speed and voltage controllers are implemented as conventional PI controllers The difference between the actual and required speed voltage is the input to the PI controller Using this difference the PI controller controls the duty cycle of PWM pulses fed to the variable DC link six step inverter corresponding to the voltage amplitude required to keep the desired speed See Figure 2 7 Hall Sensors Figure 2 7 Speed Control The speed controller calculates output voltage u t using a proportional integral PI algorithm in accordance with the following equations uite Ka x eoa 2 1 After transformation to a discrete time domain using an integral approximation by a Backward Euler method we get the following equations for the numerical PI controller calculation u k up k u k 2 2 up k K e k 2 3 T u k uk 1 Kur ek 2 4 I where e t Input error in time t Up k Proportional output portion in step k e k Input error in step k u k Integral output portion
3. 14 025A full scale In a 25 ambient operation at up to 9A continuous RMS 12A for 10 seconds output current is within the board s thermal limits Input connections are made via 40 pin ribbon cable connector J201 Power connections to the motor are made on a 3 way output connector J202 Phase A phase B and phase C are labeled on the board The input current requirements are met by a single DC power supply capable of supplying 5A however it is recommended to use a more powerful supply The voltage requirements are met by a power supply of 12V 42V The voltage should be within these limits The board will sustain at least 9V with maximum 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 25 Hardware of 50V depending on the populated components rating The input power is supplied by means of a 2 1mm jack connector J206 Table 4 1 Electrical Characteristics of the Power Stage Characteristic Symbol Min Typ Max Units Power Supply Voltage Vdc 9 12 24 42 50 V Quiescent Current loc 1 7 mA Quiescent Current 5V Generation on lccsv 4 8 mA Quiescent Current 15V Generation on locisv 5 9 mA Quiescent Current 5V 15V Generation on Iccsp e 8 9 mA Quiescent Current 5V 15V Drivers On Signal ICCALL 30 0 mA Min Logic 1 Input Voltage Vin 2 4 V Max Logic 0 Input Voltage VIL
4. Predriver ADC Voltage current 3 ph Power Stage with AD Advance cz DC DC Inverter Lite Commutation peo MOSFET Handler E Predriver Voltage PI Controller Desired voltage Speed PI Controller speed Speed Calculation Desired speed Speed command E State Machine GPIO BO 3 phase Inverter Interrupt Predriver on off Figure 3 1 System Concept 3 3 Control Process The state of the user interface is scanned periodically while the speed of the motor is measured on each new arriving edge from the Hall sensors only one phase is used for speed measurement The speed command is calculated according to the state of the control signals Start Stop Speed from FreeMASTER Then the speed command is processed by means of the speed ramp algorithm The comparison between the actual speed command obtained from the ramp algorithm output and the measured speed generates a speed error The speed error is input to the speed PI controller generating a new desired voltage level for the voltage PI controller The ADC is used to measure voltage at the variable DC link six step inverter output and a digital filter is applied to this value Then the filtered voltage is fed to the voltage PI controller The comparison between the measured and desired voltages generates a voltage error The voltage error is input to the voltage PI controller generating a new duty cycle for the 3 Phase BLDC
5. The MOSFET pre drivers are turned off by GPIO BO The required speed and desired variable DC link six step inverter output voltage variables are reset If the switch is turned off and no undervoltage overvoltage or overcurrent condition is present the INIT state is entered 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 34 Freescale Semiconductor Scaling of Quantities 5 4 Scaling of Quantities The BLDC motor control application uses a fractional representation for all real quantities except time The N bit signed fractional format is represented using 1 N 1 format 1 sign bit N 1 fractional bits Signed fractional numbers SF lie in the following range N 1 1 0 lt SF lt 1 0 2 5 1 For word and long word signed fractions the most negative number that can be represented is 1 0 whose internal representation is 8000 and 80000000 respectively The most positive word is 7FFF or 1 0 2715 and the most positive long word is 7FFFFFFF or 1 0 2 31 The following equation shows the relationship between real and fractional representations 2 Real Value Fractional Value 2 dp ET Real Quantity Range 5 2 where e Fractional Value is a fractional representation of the real value Frac16 e Real Value is the real value of the quantity V A RPM etc e Real Quantity Range is the maximum range of the quantity defined in the application V A RPM etc 5 4 1 V
6. 1 1 2 2 1 2 2 2 3 2 4 3 1 3 2 3 3 4 1 4 2 4 3 4 4 5 1 5 2 5 2 1 5 2 2 523 5 2 4 5 3 5 3 1 5 3 2 5 3 3 5 3 3 1 5 3 3 2 Chapter 1 Introduction SEE PEPE EEE EE PET ETE SETTET TER Freescale Controller Advantages and Features erre Chapter 2 Control Theory EE EEE TE ETT NE E AN Rue ddr aud RHA AE BLDC Motor Control Using DC DC Inverter an aaa eh Jiu EE e a 12 512 5517111 07 212215 NE eed o EEE EUTIN d deeds Bee ee TRETEN Chapter 3 System Concept TEEN CSI 4 dae 49 44 EE EN ESE OSD BROS op ea go EE ERE EE NER rs EET SE EE TET HE ERE FE NE ER Chapter 4 Hardware Hardware Implementation PRE EE EE PENE EE MC56F8013 Controller Board REESE EN EEE 3 Phase Power Stage with DC DC Inverter Lite nennen Motor Specifications Example iiis rer Chapter 5 Software Design ION PET rere Nain Data Flow Chait ee ee eh E AE RR ddr dec o ER RC dr ERLITTEN eier Voltage gk ee ee ee ee ee COIN EE EE ERU RUBUS EEEEEES IE ERE ui Ve OG Calculo RETTE EE ET p IOS IRI EPOR ESPERE TRE dd oid Software Implementation m er r e eC LEUTE jo igo REE ee ee ee ee ee eee ee Dive Siite Sy ee he Re ee ee 1 ig RE TET er eee ee ee RE ere ee ee BTUPPED DIE Leer bee E ee et RE el 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor B O Table of Contents 5333 RUNNING es EEE NE TEEN RE bud TP ETE 32 5 3 3 4 FAULT o PTT 32 OH SHEETS REE EVE een l
7. 250 to 4700 RPM The timer frequency is derived from the 32MHz bus clock by applying the divider For 4MHz the divider is 8 and for 250kHz it is 128 So this divider is adjusted by the current speed The motor starts with the divider at 128 allowing the speed to be measurable from 250 RPM As the speed goes up the divider is switched to 8 at the 3700 RPM threshold The system keeps this divider within the range up to 38000 RPM When the speed goes down the divider is switched to 128 at the 4200 RPM threshold 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 30 Freescale Semiconductor Software Implementation 5 3 Software Implementation The general software diagram incorporates the main routine Main entered from reset and the interrupt states see Figure 5 3 The main routine initializes the digital signal controller and the application then it enters an infinite background loop The background loop contains an application state machine The following interrupt service routines are utilized e PWM reload voltage PI controller calculation and ADC references processing PWM update e ADC conversion complete reads and filters measured values braking resistance and fault control e Timer 0 input capture and overflow commutation and speed calculation e GPIO B5 and B2 commutation e Timer 2 compare speed PI controller calculation ramp calculation Timer 1 compare commutation advance e SCI services
8. 46 Freescale Semiconductor Appendix A References The following documents can be found on the Freescale web site http www freescale com 1 MC56F8013 Controller Board User s Manual Freescale Semiconductor 2 3 Phase Power Stage with DC DC Inverter Lite User s Manual TPPSDDILUM Freescale Semiconductor 3 56F8013 Data Sheet MC56F8013 Freescale Semiconductor 4 CodeWarrior Development Studio for Freescale DSP56800 E Digital Signal Controllers Metrowerks 5 FreeMASTER for Embedded Applications Freescale Semiconductor 6 DSP56800E Quick Start User s Manual Freescale Semiconductor 7 56F83xx Motor Control Library Reference Manual Freescale Semiconductor 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 47 References 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 48 Freescale Semiconductor Appendix B Glossary AC alternating current ADC analog to digital converter brush a component transferring electrical power from non rotational terminals mounted on the stator to the rotor BLDC brushless direct current motor commutator A mechanical device alternating DC current in a DC commutator motor and providing rotation of DC commutator motor COP computer operating properly watchdog timer DC direct current DC DC or variable DC link six step Inverter power electronics module that converts DC voltage level to a d
9. ADCs supporting two simultaneous conversions ADC and PWM modules can be synchronized e One dedicated 16 bit general purpose quad timer module One serial peripheral interface SPI One serial communications interface SCI with LIN slave functionality e Oneinter integrated circuit ISC port e On board 3 3V to 2 5V voltage regulator for powering internal logic and memories 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 7 Introduction Integrated power on reset and low voltage interrupt module All pins multiplexed with general purpose input output GPIO pins Computer operating properly COP watchdog timer External reset input pin for hardware reset JTAG On Chip Emulation OnCE module for unobtrusive processor speed independent debugging Phase locked loop PLL based frequency synthesizer for the digital signal controller core clock with on chip relaxation oscillator Table 1 1 Memory Configuration Memory Type MC56F8013 MC56F8014 Program Flash 16 Kbyte 16 Kbyte Unified Data Program RAM 4 Kbyte 4 Kbyte BLDC motor control benefits greatly from the flexible PWM module fast ADC and quad timer module The PWM offers flexibility in its configuration enabling efficient control of the BLDC motor The PWM block has the following features Three complementary PWM signal pairs six independent PWM signals or a combination Complementary channel opera
10. Drive Using Variable DC Link Six Step Inverter Rev 1 20 Freescale Semiconductor Control Process variable DC link six step inverter The duty cycle value creates the PWM output for the variable DC link six step inverter and the commutation algorithm creates the output signals for the 3 phase inverter The Hall sensor signals are scanned independently of the speed control Each new arriving edge of any Hall sensor signal calls the interrupt routine providing the commutation algorithm From a certain speed level the routine determines if the incoming Hall sensor edge is correct by comparing it with a predicted signal As there is a delay between the Hall sensor edge and current commutation the current is not symmetrical To keep the current symmetrical a so called commutation advance is generated The commutation is applied using a timer countdown The timer countdown period is calculated using the time between two particular commutation edges in the previous step i e there is a table of times for each commutation sector Owing to motor geometry inaccuracy Hall sensors and winding position it is necessary to store timing information for each commutation sector In the case of a higher voltage at the variable DC link six step inverter input the brake resistance is turned on to reduce voltage When the voltage reaches a normal level the brake resistance is turned off In the case of overvoltage undervoltage overcurrent or incorrect c
11. Hall sensors signals and evaluates the rotor position Clears GPIO B pending flags Initializes timer 2 for ramp and speed control algorithms Initializes the speed PI controllers parameters Initializes FreeMASTER Pre sets the first state as the INIT state Enables the interrupts 5 3 2 Interrupts The interrupts have the following functions 32 PWM reload interrupt triggered every PWM reload On an even occurrence the ADC zero references are updated in the ADC offset registers and the voltage PI controller is calculated PWM channels 4 and 5 are updated by the duty cycle calculated by the PI controller The ADC is enabled so as to start in the next state On an odd occurrence the voltage and current ADC zero references are read and filtered ADC conversion complete interrupt the ADC is stopped for the next state The variable DC link six step inverter output voltage is read and filtered Then depending on the odd or event state either the DC bus input voltage or the motor current is read and filtered The overvoltage and undervoltage flags are generated according to the measured voltage level and or the overcurrent flag is generated according to the measured motor current level Brake resistance is turned on and off depending on the DC bus voltage level Quad timer 0 interrupt this interrupt has two sources One of them is the overflow event In this event the routine will remember that the timer overflowed as information f
12. communication with the FreeMASTER software Reset Initialization Main loop State Machine Figure 5 3 State Diagram General Overview 5 3 1 Initialization The Main routine initializes the DSP e Disables interrupts e Initializes PLL e Disables COP and LVI e Initializes the system integration module enables PWM SCI timer ADC modules connects the timer 3 input to the PWM reload sync signal Sets the timer clock source to 1x bus clock Sets the PWM clock source to 3x bus clock e Initializes GPIO A and B modules GPIO A6 and B3 as outputs for PWM 4 and 5 MOSFETs GPIO B2 and B5 as inputs for Hall sensor signals GPIO BO as the output for the brake resistance control 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 31 Software Design Initializes the SCI for FreeMASTER communication Initializes the interrupt controller Initializes the ADC Initializes timer 3 for ADC sync to PWM reload Initializes timer 1 for commutation advance Initializes timer 0 for commutation and speed evaluation Initializes the PWM module Edged aligned independent PWM mode positive polarity PWM modulus 960 defines the PWM frequency as 100kHz PWM reload every opportunity Channels 0 3 for the 3 phase inverter MOSFETs Channels 4 5 for the variable DC link six step inverter MOSFETs Initializes the voltage PI controller parameters Reads the
13. in step k w k Desired value in step k u k 1 Integral output portion in step k 1 m k Measured value in step k Tj Integral time constant u t Controller output in time t T Sampling time uk Controller output in step k Kc Controller gain 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 16 Freescale Semiconductor Speed and Voltage Control The voltage controller calculates the output PWM duty cycle for the variable DC link six step inverter using the same proportional integral PI algorithm as the speed controller 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 17 errr Control Theory 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 18 Freescale Semiconductor Chapter 3 System Concept 3 1 System Specification The system is designed to drive a 3 phase BLDC motor The application meets the following performance specification e Voltage control of BLDC motor using Hall sensors Targeted at the MC56F8013 controller board e Running on 3 Phase Power Stage with DC DC Inverter Lite e Control technique incorporating Voltage BLDC motor control using variable DC link six step inverter with voltage closed loop Closed loop BLDC motor speed control Both directions of rotation however because an impeller is used in the application the FreeMASTER page is locked to one direction only Both motor and generator modes
14. let you specify complex break conditions easily and execute your software at full speed until the break conditions are satisfied The ability to examine and modify all user accessible registers memory and peripherals through the OnCE port simplifies considerably the task of the developer e To serve as a platform for hardware development The hardware platform enables external hardware modules to be connected The OnCE port s unobtrusive design means all of the memory on the digital signal controller chip is available to the user The MC56F8013 Controller Board facilitates the evaluation of various features present in the MC56F8013 The MC56F8013 Controller Board can be used to develop real time software and hardware products based on the MC56F8013 The MC56F8013 Controller Board provides the features necessary to write and debug software demonstrate the functionality of that software and to interface with the customer s application specific device s The MC56F8013 Controller Board is flexible enough to allow full exploitation of the MC56F8013 s features to optimize the performance of the user s end product See Figure 4 2 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 24 Freescale Semiconductor 3 Phase Power Stage with DC DC Inverter Lite MC56F8013 ABO PWN HEADER HEADER gt PWM LEDs JTAG ONCE PWM GPIO PA gt UNES GPIO PD B2 B4 B5 B6 expansion ADC GPIO PC X connector
15. level This variable DC link six step inverter can also work in the opposite direction i e during braking it can transfer energy to the power supply s input voltage level To reduce the load voltage level during motor braking the DCDC Bottom MOSFET is used If this MOSFET is turned on the inductor is charged In the instant when the MOSFET is turned off the energy accumulated in the inductor is transferred to the variable DC link six step inverter s input This temporarily causes a higher voltage at the input For longer operations the input capacitor will not absorb all the energy and the input voltage will be higher In this case care must be taken and the braking MOSFET must be turned on while the voltage is higher to reduce the voltage to a safe level The bottom MOSFET of the variable DC link six step inverter operates in a different way to the top one i e whereas the top MOSFET can be switched from 0 to 100 of the duty cycle the bottom one cannot The bottom MOSFET can only be switched from 0 to a certain percentage because the inductor is discharged when the MOSFET is turned off This maximum duty cycle depends on the voltages at both the input and the output The 3 phase inverter energizes two BLDC motor phases at the same time The third phase is not powered see Figure 2 2 Thus we have six voltage vectors that may be applied to the BLDC motor 2 3 Commutation Commutation provides the creation of a rotation field As exp
16. of 8 5 ADC clock cycles 8 5 x 187ns 1 59ms Additional conversion time of six ADC clock cycles 6 x 187ns 1 125ms Eight conversions in 26 5 ADC clock cycles 26 5 x 187ns 4 97ms using parallel mode Ability to use the SYNC input signal to synchronize with the PWM provided the integration allows the PWM to trigger a timer channel connected to the SYNC input Ability to sequentially scan and store up to eight measurements Ability to scan and store up to four measurements on each of two ADCs operating simultaneously and in parallel Ability to scan and store up to four measurements on each of two ADCs operating asynchronously to each other in parallel Interrupt generating capabilities at the end of a scan when out of range limit is exceeded and on Zero crossing Optional sample correction by subtracting a pre programmed offset value Signed or unsigned result Single ended or differential inputs PWM outputs with hysteresis for three of the analog inputs The ADC is used to measure DC bus voltage variable DC link six step inverter output voltage DC bus current and 0 2V voltage and 1 65V current references The application uses the ADC block in simultaneous mode scan It is synchronized to the PWM pulses This configuration allows the simultaneous conversion of the required analog values of current and voltage within the required time The quad timer is an extremely flexible module providing all required services relating to ti
17. watched at very low speeds because of the RS232 serial communication speed limitation The FreeMASTER software Control Page is illustrated in Figure 6 1 The profiles of the required and actual speeds are available in the Speed Scope window 38 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor Chapter 6 Application Setup 6 1 Application Description The application runs on the Freescale MC56F8013 The software generates all signals needed to control the variable DC link six step inverter and 3 phase inverter according to the user required inputs measured and calculated signals The concept of the BLDC drive incorporates the following hardware components e BLDC motor set e 3 Phase Power Stage with DC DC Inverter Lite e MC56F8013 Controller Board The BLDC motor incorporates a 3 phase 24V BLDC motor with an attached high speed impeller The BLDC motor has two poles The Hall sensors are mounted inside the motor The detailed motor specifications are listed in Table 4 2 The drive can be controlled from the FreeMASTER software only To start stop the drive application click on the On Off switch e Set the required speed by clicking on the speed gauge Measured quantities e DC bus voltage s Motor current e Rotor speed The faults used for drive protection e Overvoltage s Undervoltage e Overcurrent e Hall sensors cable error 6 1 1 Control Process After reset the drive ent
18. with DC DC Inverter Lite Described in the 3 Phase Power Stage with DC DC Inverter User s Manual A detailed description of each individual board can be found in the appropriate user manual or on the Freescale web site http www freescale com The user manuals include a schematic of the board a description of individual function blocks and a bill of materials parts list 4 2 MC56F8013 Controller Board The MC56F8013 controller board is based on an optimized PCB and power supply design It demonstrates the abilities of the MC56F8013 and provides a hardware tool to help in the development of applications using the MC56F8013 The MC56F8013 controller board is an evaluation module type of board it includes an MC56F8013 part encoder interface tacho generator interface communication options digital and analog power supplies and peripheral expansion connectors The expansion connectors are for signal monitoring and user feature expandability Test pads are provided for monitoring critical signals and voltage levels The MC56F8013 controller board is designed for the following purposes s To allow new users to become familiar with the features of the MC56F801x architecture To serve as a platform for real time software development The tool suite allows you to develop and simulate routines download the software to on chip memory run the software and debug it using a debugger via the JTAG OnCE port The breakpoint features of the ONCE port
19. 0 8 V Input Logic Resistance Rin 4 7 kQ Analog Output Range Vout 0 3 3 V Bus Current Sense Voltage Isense 118 mV A Bus Current Sense Offset loffset 1 65 V Bus Voltage Sense Voltage VBus 153 E mV V Bus Voltage Sense Offset Voffset 0 2 V Power MOSFET On Resistance Rps on 0 25 0 85 1 4 mQ Continuous Output Current Ip 9 12 A Pulsed Output Current IpM 50 A Total Power Dissipation per MOSFET Pp 1 85 3 75 W Required Dead Time generated by processor tor 200 400 ns 1 Measured with the input power of 24V 2 The values are measured at 25 C for other temperatures the values may be different 4 4 Motor Specifications Example The motor used in this application is a high speed low inductance 24V BLDC motor equipped with Hall sensors The motor has the following specifications Table 4 2 Specifications of the Motor and Hall Sensors Motor Tvpe 3 Phase BLDC Motor ype 2 Poles Motor Specification Speed Range lt 38000 RPM Line Voltage 24V Phase Current lt 5A mm Sensor 1 Type 3 Phase Hall Sensors Position Sensor Specification Sensor 2 Type None 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 26 Freescale Semiconductor Chapter 5 Software Design 5 1 Introduction This section describes the design of the drive s software blocks The software description comprises these topics e Main Data Flow Ch
20. 2 to connect PB1 to UNI 3 29 BRAKE e Remove R45 to disconnect SW3 and 3 3V pullup voltage e Remove R41 to disconnect SW2 and 3 3V pullup voltage e Remove R62 Q1 to disconnect fault and 3 3V pullup voltage Table 6 3 3 Phase Power Stage with DC DC Inverter Lite Jumper Options Function Connections JP401 Pre driver enabled by the UNI 3 signal 2 3 JP501 5V voltage generation enabled closed JP502 15V voltage generation enabled closed 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 44 Freescale Semiconductor Project Files CAUTION Do not enable 15V generation on the 3 Phase Power Stage with DC DC Inverter without enabling 5V generation The gate signals use buffers to convert from 3 3V logic to 5V logic As the brake resistance pre driver is always enabled the absence of 5V could turn on the brake resistance Some signals must be swapped on the UNI 3 cable according to Table 6 4 Table 6 4 UNI 3 Cable changes Power Stage Controller Board 9 39 11 40 31 9 33 11 39 Not connected 40 Not connected Not connected 31 Not connected 33 6 3 Project Files The 3 Phase BLDC drive using variable DC link six step inverter application is composed of the following files e bldc_hall_56F8013_qs21 bldc_hall_56F8013 c main program e W5idc hall 56F8013 qs21Ybldc hall 56F8013 qs21 mcp application project file e _ bldc_hall_56F801
21. 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Designer Reference Manual 56800E 16 bit Digital Signal Controllers DRMO78 Rev 1 05 2006 X I freescale com 2 freescale semiconductor 3 Phase BLDC Drive Using DC DC Inverter Designer Reference Manual by Jaroslav Musil Freescale Czech Systems Laboratories Roznov pod Radhostem Czech Republic To provide the most up to date information the revision of our documents on the World Wide Web will be the most current Your printed copy may be an earlier revision To verify you have the latest information available refer to http www freescale com The following revision history table summarizes changes contained in this document For your convenience the page number designators have been linked to the appropriate location Revision History Revision T Page Date Level Description Number s March ut 2006 0 Initial release N A Changed hybrid controller to digital signal controller Various Changed DC DC inverter to variable DC link six step inverter Various May 2006 1 Minor edits to clarify Chapter 1 7 Renamed Section 2 4 to better reflect contents and added information at end 17 of section 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 3 Revision History 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 4 Freescale Semiconductor Table of Contents 1
22. 3_qs21 ApplicationConfig appconfig h application configuration file e bldc_hall_56F8013_qs21 SystemConfig SDM_pFlash cmd linker command file for Flash e bldc_hall_56F8013_qs21 Freemaster bldc_hall_56F8013 pmp FreeMASTER software file These files are located in the application folder e ramp c h source and header files for ramp generation s MCLIB56F800E_r2 0 MCLIB_56800ESDM lib motor control algorithms library Allnecessary Quick Start resources algorithms and peripheral drivers are part ofthe application project folder Allresources are copied into the following folder under the application folder so the libraries of the DSP56800E_Quick_Start are no longer required s bldc_hall_56F8013_qs21 src include folder for general C header files e Wbldc hall 56F8013 qs21lsrelMC56F8013 folder for the device specific source files e g drivers e Widc hall 56F8013 qs21YsresupportMreemaster folder for FreeMASTER software source files 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 45 Application Setup 6 4 Application Build and Execute When building the 3 Phase BLDC drive using variable DC link six step inverter an application running from pFlash is created The project may be built by executing the Make command illustrated in Figure 6 4 This builds and links the 3 Phase BLDC drive using variable DC link six step inverter application and all required Metrowerks an
23. 6200 RPM so the software maximum speed is set with small reserve as vmax 38000RPM 5 5 And for the lower speed maximum use the maximum higher speed divided by 8 because a division by 8 can be performed very easily by register shifting and is not very time consuming Therefore vmax_low en 4750RPM 5 6 2 We have to know the number of Hall sensor edges per revolution The motor has one pole pair meaning six edges per revolution three rising three falling for the three Hall sensors But this application uses only one Hall sensor so there should be two edges per revolution As it is a very fast motor it is enough to use just one edge rising for the speed calculation So the final number of edges per revolution is one Therefore position difference tcd 1 5 7 3 A 16 bit timer is used meaning it overflows after 65535 increments As mentioned above for the higher speeds the 8 divider is used so the frequency is 32MHz 8 4MHz The time period for the timer overflow is then max period 16 38375ms 5 8 For the lower speed calculations the frequency is 32MHz 128 250kHz So the time period for the timer overflow is then max period low e 262 14ms 5 9 4 Knowing the maximum timer period we can determine the minimum possible speed in RPM So the minimum speed limits are men min 1 Position difference _ EE 1 2RPM i vmin 60s min ur end 60s min 16 38375ms 366 5 10
24. Inverter Lite Serial cables required for the FreeMASTER software tool only Parallel cable with JTAG converter required for the Metrowerks CodeWarrior debugging and software loading 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor Application Set Up 6 2 1 MC56F8013 Controller Board Application Setup To execute the 3 Phase BLDC drive using variable DC link six step inverter the MC56F8013 Controller Board and 3 phase Power Stage with DC DC Inverter Lite require the strap settings shown in Figure 6 3 and Table 6 2 Table 6 3 Q1 I Figure 6 3 MC56F8013 Controller Board 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 43 Application Setup Table 6 2 MC56F8013 Controller Board Jumper Options Selector Function Connections JP1 SCI Full duplex serial mode 2 3 R1 R2 RS 232 interface enabled R1 R2 present JP3 Encoder UNI 3 BEMFZCx Hall sensor 1 to PB4 Hall sensor 2 to PB5 4 5 7 8 PHBIS BEMFB I IN 1 65V current reference to ANB1 UNI 3 phase B current 4 5 d PHCIS BEMFC TEMP 0 2V v
25. Starting from any motor position without rotor alignment Minimum speed 300 RPM Maximum speed 38000 RPM e FreeMASTER software control interface motor start stop speed setup e FreeMASTER software monitor FreeMASTER software graphical control page required speed actual motor speed start stop status DC bus voltage level motor current system status FreeMASTER software speed scope observes actual and desired speeds FreeMASTER software Hall sensor scope observes actual Hall sensors state DC bus overvoltage and undervoltage overcurrent Hall sensors cable fault protection 3 2 Application Description A standard system concept is chosen for the drive see Figure 3 1 The system incorporates the following hardware boards e Power supply 24V DC 5A e 3 Phase Power Stage with DC DC Inverter Lite e BLDC motor with Hall sensors e MC56F8013 controller board The 3 Phase Power Stage with DC DC Inverter Lite runs the main control algorithm In response to the user interface and feedback signals it generates PWM signals for the variable DC link six step inverter and 3 phase output signals for a 3 phase inverter 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 19 System Concept MC56F8013 Controller Board mut o 0h GPIO_B1 m Predriver Resistance 100kHz E MOSFET Voltage level control 4 DC DC ES C p Inverter
26. art e Software Implementation e Scaling of Quantities e FreeMASTER Software 5 2 Main Data Flow Chart The control algorithm of a closed loop BLDC drive is described in Figure 5 1 The individual processes are described in the following sections 5 2 1 Speed Control Speed control starts with the mfwomegaRequiredMech variable This variable is remotely set within allowed limits by the FreeMASTER software on a PC The variable mfwomegaRequiredMech is fed to the ramp algorithm periodically performed in the timer compare interrupt It is calculated every 10ms The predefined ramp is 10000 RPM per 100ms The ramp algorithm generates the fwDesiredSpeed variable input to the speed PI controller as a reference value The measured speed provides a second input to this controller The difference between these two values is the speed error The speed PI controller generates the desired variable DC link six step inverter output voltage fwDesiredVoltage The commutation vector is calculated with respect to the polarity of the desired voltage while its absolute value is fed to the voltage PI controller as m wDesiredDCDCVoltage If the actual speed absolute value is smaller than 4600 RPM and the desired voltage is smaller than 2V the required speed is set to 0 all bottom MOSFETs are turned on and the motor is braked the muwwZeroDCDCVoltage variable is set to 1 The system contains two speed PI controllers one for the range 15000 to 40000 RPM create
27. d Quick Start libraries Jos Debug Processor Expert Data Visualization Add bldc hall 56F8013 c to Project Add Files Create Group Create Target Create Segment Overlay Create Design Export Project as GNU Makefile Check Syntax Ctrl Preprocess Precompile Compile Ctrl F7 Disassemble Ctrl Shift F7 Bring Up To Date Ctrl U Stop Build Ctrl Break Remove Object Code Ctrl Re search for Files Reset Project Entry Paths Synchronize Modification Dates Debug F5 Can t Run Ctrl F5 Set Default Project Set Default Target GCT F12 Figure 6 4 Execute Make Command To execute the 3 Phase BLDC drive using variable DC link six step inverter application select Project Debug in the CodeWarrior IDE followed by the Run command For more help with these commands refer to the CodeWarrior tutorial documentation in the following file located in the CodeWarrior installation folder lt gt Help PDF Targeting_DSP56800 pdf CodeWarrior will automatically program the internal Flash of the controller with the executable generated during Build Once the Flash is programmed with the executable code the parallel cable can be disconnected and the software remains in the Flash after a power down or reset Once the application is running connect the serial cable and run the FreeMASTER software on your PC to control the application 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1
28. d for an acceleration of 15000 RPM per 100ms and a second for the range 0 to 15000 RPM constructed with an acceleration of 10000 RPM per 300ms The speed controller is calculated every 1ms The hysteresis between these two PI controllers is 1500 RPM meaning if the speed goes up the higher speed PI controller is switched on at the threshold of 15000 RPM and when the speed goes down the lower speed PI controller is switched on at a speed of 18500 RPM 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 27 Software Design POSITION SENSOR Hall Sensors Quad Timer 1 Quad Timer 3 Timer Compare Interrupt Timer Compare Timer 0 Capture Interrupt Interrupt GPIO B2 B5 Interrupt one phase only Period Measuring muwwHallSensorsState miwDirectionSpinning muwlMeasuredPeriod Speed Calculation nn Next HS State Prediction Mask and Swap Calculation Predicted com time Cas B3 Update ES ADC Conversion Interrupt PWM Module PWM Reload Interrupt mfwDCDCVoltage Timer Compare Interrupt Brake Control A mfwOmegaDesiredMech PI Controller mwwDuty E ariable DC Link Six Step inverter duty cycle update Software Block 4 5 ae Hardware Block Figure 5 1 Main Data Flow 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 28 Freescal
29. e Requests Only Freescale Semiconductor Literature Distribution Center P O Box 5405 Denver Colorado 80217 1 800 441 2447 or 303 675 2140 Fax 303 675 2150 LDCForFreescaleSemiconductor hibbertgroup com DRMO78 Rev 1 05 2006 RoHS compliant and or Pb free versions of Freescale products have the functionality and electrical characteristics of their non RoHS compliant and or non Pb free counterparts For further information see http www freescale com or contact your Freescale sales representative For information on Freescale s Environmental Products program go to http www freescale com epp Information in this document is provided solely to enable system and software implementers to use Freescale Semiconductor products There are no express or implied copyright licenses granted hereunder to design or fabricate any integrated circuits or integrated circuits based on the information in this document Freescale Semiconductor reserves the right to make changes without further notice to any products herein Freescale Semiconductor makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does Freescale Semiconductor assume any liability arising out ofthe application or use of any product or circuit and specifically disclaims any and all liability including without limitation consequential or incidental damages Typical parameters that may be provided in Freescale Se
30. e Semiconductor Main Data Flow Chart 5 2 2 Voltage Control The voltage control is based on the PWM reload interrupt established at a frequency of 100kHz illustrated in Figure 5 2 TXNAAZRO IP kg O 1 O T O Figure 5 2 Voltage Control Scheduling As stated the PWM reload generates an interrupt every 10us The reload serves to synchronize some processes to the variable DC link six step inverter PWM period e The ADC start is situated at 1us after the beginning of every second PWM period by means of timer 3 This timer is started at the beginning of the PWM reload period When timer 3 reaches its compare period it triggers the ADC scan The PWM timer and ADC are connected on a hardware level so no software interaction is required e When the ADC measures the desired values it generates an interrupt where the measured values are filtered and stored for further processing When the PWM reload interrupt is called the muwwADCTrigger is inverted 0 1 This variable determines if the ADC is started in the current PWM period 0 and or if the voltage PI controller is calculated 1 Timer 3 does not contain any routine attached to its interrupt and serves only to start the ADC conversion precisely 90 increments after the start of the PWM period When the ADC finishes the conversion it reads and filters the measured values The ADC measurement uses only four channels in the simultaneous mode due to the shortage of time So ADC channe
31. ers the INIT state in which the application is initialized it then goes into the STOP state In the STOP state all the control signals are disabled and the motor cannot spin The operation mode can be changed to the RUN state from the FreeMASTER software by clicking on the On Off button Speed is controlled in the RUN state using the mfwomegaRequiredMech variable This variable is set within allowed limits remotely by the FreeMASTER software on PC The variable mfwOmegaRequiredMech is fed to the ramp algorithm The predefined ramp is 10000 RPM per 100ms The ramp algorithm generates the fwDesiredSpeed variable input to the speed PI controller as a reference value and a second input to this controller is the measured speed The difference between these two values is the speed error The speed PI controller generates the desired variable DC link 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 39 Application Setup six step inverter output voltage fwDesiredVoltage The commutation vector is calculated with respect to the polarity of the desired voltage while its absolute value is fed to the voltage PI controller as mfwDesiredDCDCVoltage The system measures the variable DC link six step inverter output voltage fed to the PI controller The difference between the desired voltage mfwDesiredDCDCVoltage and the measured voltage mfwDCDCVoltage is the error This controller s output is simply the duty cycle f
32. ge should be present at the variable DC link six step inverter output The following variables and peripherals are initialized e Resets the required speed and the desired variable DC link six step inverter output voltage and low speed PI controller integral portion variables e If the switch is turned on the application enters the RUNNING state At the same time the variable DC link six step inverter duty cycle variable is set to 0 the MOSFET pre drivers are switched on by GPIO BO all the bottom MOSFETS are turned on and the top MOSFETS are turned off PWM and GPIO B2 and B5 outputs are enabled and the brake resistance output pin is enabled 5 3 3 3 RUNNING State The application remains in this state as long as the switch is turned on If an undervoltage overvoltage overcurrent or Hall sensor signal fault is present the FAULT state is entered The MOSFET pre drivers are turned on In this state the inverters are controlled and the motor can be driven If the switch is turned off the application enters the STOPPED state At the same time the PWM and GPIO B2 and B5 output pins are disabled forced into tri state along with the brake resistance control pin GPIO BO 5 3 3 4 FAULT State This state is entered when a fault is generated by an overvoltage undervoltage overcurrent or Hall sensor signal In this state the PWM and GPIO B2 and B5 output pins are disabled forced into tri state along with the brake resistance control pin GPIO BO
33. ifferent DC voltage level DSC digital signal controller MC56F80x a Freescale family of 16 bit DSPs dedicated to motor control DT dead time a short time that must be inserted between the turning off of one transistor in the inverter half bridge and turning on of the complementary transistor due to the limited switching speed of the transistors duty cycle the ratio of the amount of time the signal is on to the time it is off Duty cycle is usually quoted as a percentage GPIO general purpose input output Hall sensor a position sensor giving six defined events each 60 electrical degrees per electrical revolution for a 3 phase motor interrupt a temporary break in the sequential execution of a program to respond to signals from peripheral devices by executing a subroutine I O input output interfaces between a computer system and the external world A CPU reads an input to sense the level of an external signal and writes to an output to change the level of an external signal JTAG Joint Test Action Group acronym commonly used to refer to an interface allowing on chip emulation and programming LED light emitting diode PI controller proportional integral controller PLL phase locked loop a clock generator circuit in which a voltage controlled oscillator produces an oscillation that is synchronized to a reference signal 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 F
34. isten 33 5 4 1 an e Eee EEE EEE NT TE NTT TI TEEN TERN TEN 33 5 4 2 EE RET EE RE EEE EE 33 5 4 3 aitus fi cuo os ee erst 34 5 4 4 SIE DIENEN ur rn T 34 5 5 EEE EE ee RI ORE eee ER NE 35 Chapter 6 Application Setup 6 1 Applicaton Desenplidll 2214442039 EIS COR ER Y EHE VODKA 24854691598 160 SRE RR OR 37 6 1 1 CODO PROPRES ee ee ACCRUE RD R e RR 37 6 1 2 Dive al 02 REE EEE EE ENE 38 6 2 eee Uo RET ET EEE EEE PTE SER 40 6 2 1 MC56F8013 Controller Board Application Setup sasesana eR RR Ii 41 6 3 TE shee E rer 43 6 4 Applicaton Builg and BEA een ee ah RO CUR N 44 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 6 Freescale Semiconductor Chapter 1 Introduction 1 1 Introduction This paper describes the design of a 3 phase BLDC drive using a variable DC link six step inverter based on Freescale s MC56F8013 dedicated motor control device Recently small high speed BLDC motors have become very popular in a wide application area The BLDC motor does not have a mechanical commutator and is consequently more reliable than the DC motor Small high speed BLDC motors have very low inductance compared to conventional BLDC motors When PWM control is applied to the phases of a BLDC motor the current follows the rectangular PWM voltage shape This rapidly changing current magnetizes and demagnetizes the motor iron at a frequency equal to the PWM frequency Due to magnetic hysteresis losses the motor can become hot enough
35. k Req Speed step 10k 20k Req i Speed step 10k 25k Req DC Bus Voltage V Motor Current A Speed kRPM Speed step 10k 30k Req Speed step 15k 20k Req Speed step 15k 25k Req Speed step 15k 30k Req Speed step 5k 10k Requi Speed step 7k 12k Requ Speed step 7k 17k Requ Value Speed step 7k 20k Requi K Speed step 7k 25k Requ Application Mode Running ENUM Sneed sten 7k 30k Reaui Y RUN STOP Switch Status RUN ENUM mit Actual Sneed 35002 RPM Figure 6 1 FreeMASTER Software Control Window 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 41 Application Setup 6 2 Application Set Up Figure 6 2 illustrates the hardware setup for the 3 Phase BLDC drive using variable DC link six step inverter application The controller board power stage and motor are mounted on a plexiglass board 3 ph Motor Cable MC56F8013 Controller Board 3 ph Power Stage with DC DC Inverter Figure 6 2 Setup of the BLDC Drive using DC DC Inverter For detailed information see the MC56F8013 Controller Board User s Manual and the 3 Phase Power Stage with DC DC Inverter Lite User s Manual The serial cable is needed for the FreeMASTER software control The system consists of the following components 42 High speed 24V BLDC motor MC56F8013 controller board 3 Phase Power Stage with DC DC
36. l 0 is used for the variable DC link six step inverter output voltage measurement each ADC period 50kHz and channel 1 is shared by the DC bus input voltage and motor current that are then measured at a frequency of 25kHz Channels 4 and 5 are used to measure the voltage and current zero references These two references are read and filtered until the following PWM reload interrupt when the voltage PI controller value is not calculated However the filtered references are updated in the ADC offset registers in the period when the voltage PI controller value is calculated So the variable DC link six step inverter output voltage DC bus input voltage and motor current are measured The measured values are subtracted from the measured references and then filtered The subtraction is performed by hardware using the ADC offset registers If the measured DC bus voltage is greater than 26V the braking resistance MOSFET is turned on and is turned off when the voltage falls below 25V If the voltage is higher than 25V or lower than 18V for longer than 100ms the overvoltage or undervoltage flag is generated The overcurrent protection averages the measured current over the interval of 16384 values If this averaged current is higher than 3 5A the overcurrent flag is generated 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 29 Software Design As stated the voltage PI controller calculation is performed ever
37. lained previously for proper operation of a BLDC motor it is necessary to keep the angle between the stator and rotor flux close to 90 With six step control we get a total of six possible stator flux vectors The stator flux vector must be changed at a certain rotor position The rotor position is usually sensed by Hall sensors The Hall sensors generate three signals also comprising six states Each of the Hall sensor states corresponds to a certain stator flux vector All Hall sensor states with corresponding stator flux vectors are illustrated in Figure 2 4 The same figure is illustrated in tables Table 2 1 and Table 2 2 The next two figures depict the commutation process The actual rotor position in Figure 2 5 corresponds to the Hall sensors state ABC 110 see Figure 2 4 The actual voltage pattern can be derived from the Table 2 1 Phase A is connected to the positive DC bus voltage by the transistor PWM AT phase C is connected to ground by transistor PWM CB and phase B is not powered As soon as the rotor reaches a certain position see Figure 2 5 the Hall sensor state changes its value from ABC 110 to ABC 100 From Table 2 1 a new voltage pattern is selected and applied to the BLDC motor As can be seen with a six step control technique there is no possibility of keeping the angle between the rotor flux and the stator flux precisely at 90 The real angle varies from 60 to 120 The commutation is repeated for each 60 elect
38. ll sensor edge signal is different from predicted the interrupt routine ends and no commutation is performed This means the commutation is performed as soon as the correct Hall sensor signal arrives This routine also stores in the table the time between two commutation edges Each commutation sector has its own table record If the speed is greater than 11600 RPM commutation is advanced Once the controlled commutation advance technique is turned on it is turned off when the speed goes below 8700 RPM The advance period is set by the muwwCommutat ionAdvance variable with a precision of 100ns It is set to 40us meaning the commutation is performed 40us before the commutation edge arrives It improves the motor spinning and torque efficiency This method uses timer 1 updated and synchronized on every commutation Hall sensor edge If the system does not receive the predicted commutation edge within 200 commutations a Hall sensors cable fault is generated During this period the system commutates using the timer and commutation times table 5 2 4 Velocity Calculation The Hall sensors generate streams of pulses captured phase A by the timer 0 input capture function The speed can be calculated knowing the timer frequency and the time between two Hall sensor edges The application uses the two timers frequencies to enlarge the RPM range The first frequency is 4MHz for the range 3700 to 38000 RPM the second frequency is 250kHz for the range
39. me events It has the following features Freescale Semiconductor Four 16 bit counters timers Count up down Counters are cascadable Programmable count modulus Maximum count rate equal to the peripheral clock 2 when counting external events Maximum count rate equal to the peripheral clock 1 when using internal clocks Count once or repeatedly Counters are preloadable Counters can share available input pins Each counter has a separate prescaler Each counter has capture and compare capability 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Introduction The application uses four channels of the quad timer for e PWM to ADC synchronization s Hall sensor edge scanning used for speed calculation e System base for ramp and speed control e Commutation advance control 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 10 Freescale Semiconductor Chapter 2 Control Theory 2 1 BLDC Motor A brushless DC BLDC motor is a rotating electric machine where the stator is a classic 3 phase stator like that of an induction motor and the rotor has surface mounted permanent magnets see Figure 2 1 Stator Stator winding in slots Shaft Rotor Air gap Permanent magnets Figure 2 1 BLDC Motor Cross Section In this respect the BLDC motor is equivalent to a reversed DC commutator motor in which the magnet rotates while the conductors remain stationary Inthe DC commutator motor
40. miconductor data sheets and or specifications can and do vary in different applications and actual performance may vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts Freescale Semiconductor does not convey any license under its patent rights nor the rights of others Freescale Semiconductor products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the Freescale Semiconductor product could create a situation where personal injury or death may occur Should Buyer purchase or use Freescale Semiconductor products for any such unintended or unauthorized application Buyer shall indemnify and hold Freescale Semiconductor and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that Freescale Semiconductor was negligent regarding the design or manufacture of the part Freescale and the Freescale logo are trademarks of Freescale Semiconductor Inc All other product or service names are the property of their respective owners F
41. oltage Scaling The DC bus voltage and variable DC link six step inverter output voltage sense is defined by the following equation VMEASURED voltage 32767 5 3 MAX Where voltage variable of measured voltage VMEASURED measured voltage Vmax max measurable voltage Vmax 31V for the 3 Phase Power Stage with DC DC Inverter Lite 5 4 2 Current Scaling The motor current sense is defined by the following equation I current EE 32767 5 4 MAX Where current variable of measured current IMEASURED Measured current Imax max measurable current Imax 14 025A for the 3 Phase Power Stage with DC DC Inverter Lite 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 35 Software Design 5 4 3 PI Controller Parameters The PI controller parameters consists of the gain and gain scale parameters of the proportional and integral constants The proportional or integral gain parameter lies in the fractional number 0 to 1 representing 0 to 32767 and the gain scale parameter shifts the particular gain to the right if positive or to the left if negative The gain scale number represents the number of shifts The limit parameters represent the minimum and maximum outputs from the PI controller The output will be within these limits 5 4 4 Speed Calculation The speed coefficient scaling is as follows 1 The maximum speed of the motor is 3
42. oltage reference to ANB2 UNI 3 phase C current 7 8 PHBIS BEMFB 1 65V current reference phase B current measurement selected 4 5 dis PHCIS BEMFC 0 2V voltage reference phase C current measurement selected 7 8 J8 START Switch START switch disconnected from PB3 open J9 PFC PWM UNI 3 PFC PWM disconnected from PB2 open Ae EEE R RARE USER LED output disconnected open UNI 3 BRAKE output disconnected open J11 TACHO TEMP DC bus voltage measurement UNI 3 TEMP gt ANA2 selected 1 2 J14 Tacho dynamo measurement Tacho dynamo input gt digital output selected 2 3 J15 Tacho generator Tacho generator digital output disconnected from PB4 open J16 UNI 3 45V CB digital power supply from UNI 3 5V closed J18 UNI 3 15V CB analog power supply from UNI 3 15V closed J17 WP Serial EEPROM memory is write protected open J20 SCL Serial EEPROM memory SCL input disconnected from PBO open J21 SDA Serial EEPROM memory SDA I O disconnected from PB1 open As the MC56F8013 Controller Board was not designed exactly for this application some additional operations must be provided e Wire connection between JP3 1 and J9 2 to connect Hall sensor 3 to PB2 e Wire connection between JP4 6 and J2 1 to connect PBO to UNI 3 32 DRV EN e Wire connection between JP5 6 and J3 8 to connect PAG to UNI 3 39 PWM CT e Wire connection between JP5 9 and J2 4 to connect PB3 to UNI 3 40 PWM CB e Wire connection between J10 3 and J2
43. ommutation edges within 200 commutations the signals for the variable DC link six step inverter and for the 3 phase inverter are disabled and the fault state is displayed 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 21 System Concept 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 22 Freescale Semiconductor Chapter 4 Hardware 4 1 Hardware Implementation The application runs on Freescale s motor control MC56F8013 Controller Board Freescale s 3 Phase Power Stage with DC DC Inverter Lite and a 24V BLDC motor with Hall sensors and high speed impeller Both boards are integral parts of Freescale s set of embedded motion control development tools The application hardware system configuration is shown in Figure 4 1 MC56F8013 Controller Board 3 ph Power Stage with DC DC Inverter Lite Jack 2 1mm Power Input 4V15 4A l RS232 Figure 4 1 Hardware System Configuration 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 23 Hardware All system parts are supplied and documented in these references e MC56F8013 Controller Board Using Freescale s MC56F8013 as the controller Supplied as MC56F8013 Controller Board Described in the MC56F8013 Controller Board User s Manual e 3 Phase Power Stage with DC DC Inverter Lite Using Freescale s MC33883 MOSFET pre drivers Supplied as 3 Phase Power Stage
44. or further speed calculation The other source is the input capture signal This event is used for commutation and also for the speed calculation This routine also saves the Hall sensor edge time of each sensor and uses it to calculate the time of the next advanced commutation GPIO B interrupt this interrupt routine has two sources pins 5 and 2 Both are connected to the Hall sensor signals and serve for commutation 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor Software Implementation e Quad timer 2 interrupt this interrupt is generated every 1ms It generates the speed ramp and calculates the speed PI controller It also turns on and off the commutation control features such as prediction of the next Hall sensor state and commutation advance control e Quad timer 1 interrupt this interrupt occurs when the timer reaches the preset compare value loaded in the quad timer 0 interrupt This compare event causes advanced commutation and calculates the time of the next advanced commutation for the case where the Hall sensor edge does not arrive in the next state 5 3 3 Drive State Machine The drive can be in one of the following states illustrated in Figure 5 4 also showing transition conditions among the drive states E i Reset mintSwitchState 1 mintSwitchState 0 mfwOverCurrent lt TRESHOLD OVERCURRENT mwwOverVoltageCounter 0 mwwUnderVoltageCounter 0 mintS
45. or the variable DC link six step inverter MOSFETs mwwDuty Its absolute value is written either to PWM channel 4 or 5 If it is positive channel 4 is loaded with the duty cycle value and channel 5 is loaded with 0 vice versa if it is negative According to the Hall sensor state and the desired direction of spinning the MOSFETSs of the 3 phase inverter are turned on and off and the motor spins 6 1 2 Drive Protection The DC bus voltage and motor current are measured during the control process They protect the drive from overvoltage undervoltage and overcurrent All protection is performed by software The Hall sensor cable signals are read during running If the sensors return an unidentified commutation vector a Hall sensor cable fault is generated If any of the above mentioned faults occur the variable DC link six step inverter and 3 phase inverter control signals are disabled to protect the drive and the application enters the FAULT state At the same time the MOSFET pre drivers are disabled If no overvoltage undervoltage or overcurrent condition is present the application can be switched from the FAULT state to the STOP state by switching off the switch Table 6 1 Motor Application States Application State Motor State Pre driver State Gate Signals Init Stopped gates tri stated Disabled Tri stated Stopped Stopped gates tri stated Disabled Tri stated Running Spinning gates active Enabled Logically active Fa
46. reescale Semiconductor Inc 2006 All rights reserved ey 2 freescale semiconductor
47. reescale Semiconductor 49 Glossary PWM pulse width modulation Quad timer a module with four 16 bit timers reset to force a device to a known condition RPM revolutions per minute SCI serial communication interface module a module that supports asynchronous communication software instructions and data that control the operation of a microcontroller 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 50 Freescale Semiconductor How to Reach Us Home Page www freescale com E mail support freescale com USA Europe or Locations Not Listed Freescale Semiconductor Technical Information Center CH370 1300 N Alma School Road Chandler Arizona 85224 1 800 521 6274 or 1 480 768 2130 support freescale com Europe Middle East and Africa Freescale Halbleiter Deutschland GmbH Technical Information Center Schatzbogen 7 81829 Muenchen Germany 44 1296 380 456 English 46 8 52200080 English 49 89 92103 559 German 33 1 69 35 48 48 French support O freescale com Japan Freescale Semiconductor Japan Ltd Headquarters ARCO Tower 15F 1 8 1 Shimo Meguro Meguro ku Tokyo 153 0064 Japan 0120 191014 or 81 3 5437 9125 support japan O freescale com Asia Pacific Freescale Semiconductor Hong Kong Ltd Technical Information Center 2 Dai King Street Tai Po Industrial Estate Tai Po N T Hong Kong 800 2666 8080 support asia freescale com For Literatur
48. rical degrees The angular time accuracy of the commutation event is critical any deviation causes torque ripples leading to variations in speed 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 13 Control Theory Phase C Phase B ABC 100 ABC 001 ABC 101 ABC Hall Sensors Output Figure 2 4 Stator Flux Vectors with Six Step Control Table 2 1 Commutation Sequence for Clockwise Rotation Hall Sensor A Hall Sensor B Hall Sensor C Phase A Phase B Phase C 1 0 0 VpcB VpcB NC 1 0 1 NC VpcB VpcB 0 0 1 VpcB NC VpcB 0 1 1 VpcB VpcB NC 0 1 0 NC VpcB VpcB 1 1 0 VpcB NC VpcB Table 2 2 Commutation Sequence for Counterclockwise Rotation Hall Sensor A Hall Sensor B Hall Sensor C Phase A Phase B Phase C 1 0 0 VpcB VpcB NC 1 1 0 VpcB NC VpcB 0 1 0 NC VpcB VpcB 0 1 1 VocB VpcB NC 0 0 1 VpcB NC VpcB 1 0 1 NC VpcB VpcB 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor Commutation VCC i d Phase A Phase B d Phase C 3 Actual flux vector Figure 2 5 Situation Right Before Commutation VCC i Ss pr Phase A C Phase C J Ne i PSR B New flux vector Figure 2 6 Situation Right After Commutation 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev
49. the MOSFETs of the 3 phase inverter However there are small high speed BLDC motors with very low inductance If PWM is applied to the MOSFETs of the 3 phase inverter of such a motor the current waveform will copy the PWM voltage waveform Such a current waveform will rapidly and frequently magnetize and demagnetize the metal causing huge thermal losses due to magnetic hysteresis Therefore these BLDC motors require a special power stage with a variable DC link six step inverter illustrated in Figure 2 3 The power stage uses six power transistors fully turned on off to control the commutation The voltage level is controlled by two transistors in the variable DC link six step inverter Brake DC DC Inverter V_PWR Q DCDC_Top Inverter PWM AT PWM_BT PWM_CT DCDC_Botom PWM_AB PWM_BB PWM_CB GND_PWR Y Y Y Phase A Phase B Phase C Figure 2 3 3 Phase BLDC Power Stage with a Variable DC Link Six Step Inverter 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 12 Freescale Semiconductor Commutation The variable DC link six step inverter controls the voltage on the motor while commutation is performed by the 3 phase inverter The variable DC link six step inverter output is controlled by switching the DCDC_Top MOSFET Figure 2 3 Thus the variable DC link six step inverter uses the inductor L and the capacitor C to keep output voltage at the desired
50. the current polarity is altered by the commutator and brushes On the contrary in the brushless DC motor the polarity reversal is performed by power transistors switching in synchronization with the rotor position Therefore BLDC motors often incorporate either internal or external position sensors to discern the actual rotor position alternatively the position can be detected without sensors 2 2 BLDC Motor Control Using a Variable DC Link Six Step Inverter The BLDC motor is driven by rectangular voltage waveforms coupled with the given rotor position see Figure 2 2 The generated stator flux interacts with the rotor flux generated by a rotor magnet defining the torque and thus speed of the motor The voltage waveforms must be properly applied to the two phases of the 3 phase winding system to keep the angle between the stator flux and the rotor flux close to 90 to generate maximum torque To achieve this the motor requires electronic control for proper operation 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 11 Control Theory Voltage Uscs Phase A Unos Uscs Phase B Uncs Uscg Phase C Ubos 30 60 90 120 150 180 210 240 270 300 330 Electrical angle 3 phase Figure 2 2 Voltage Waveforms Applied To the 3 phase BLDC Motor For standard BLDC motors a power stage with a 3 phase inverter is used Control is provided by applying PWM waveforms to
51. tion features Independent top and bottom dead time insertion 56F8013 Separate top and bottom pulse width correction via current status inputs or software Separate top and bottom polarity control Edge aligned or center aligned PWM reference signals 15 bit resolution Half cycle reload capability Integral reload rates from one to sixteen periods Mask swap capability Individual software controlled PWM output Programmable fault protection Polarity control 10mA or 16mA current sink capability on PWM pins Write protectable registers The PWM module is capable of controlling two PWM signals for the variable DC link six step inverter It can be configured to a switching frequency of 100kHz with a resolution of 1 in 960 i e almost 10 bit The PWM module generates its reload signal it can then be used to synchronize other modules to the PWM The four remaining PWM channels are used for phase A and phase B of the 3 phase inverter which takes care of the motor commutation using the mask feature of the DSC Phase C is controlled by two GPIO pins 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor Freescale Controller Advantages and Features The ADC module has the following features 12 bit resolution Dual ADCs per module three input channels per ADC Maximum ADC clock frequency of 5 33MHz with a 187ns period Sampling rate of up to 1 78 million samples per second Single conversion time
52. to be damaged and the high current ripple will cause other losses Because of the special control required by the motor the method adopted in this reference design uses a variable DC link six step inverter r to generate the desired voltage for the motor The motor then requires only a conventional three phase inverter for commutation The concept of the application is a high speed BLDC motor with closed loop speed control It serves as a design example of a 3 phase BLDC drive with variable DC link six step inverter using a Freescale digital signal controller This reference design includes basic motor theory system design concept hardware implementation and the software design including the FreeMASTER software visualization tool 1 2 Freescale Controller Advantages and Features The Freescale MC56F801x family is well suited to digital motor control combining the DSP s calculation capability with the MCU s controller features on a single chip These digital signal controllers offer many dedicated peripherals such as pulse width modulation PWM modules analog to digital converters ADC timers communication peripherals SCI SPI ISC and on board Flash and RAM The MC56F801x family members provide the following peripheral blocks e One PWM module although with a limited pinout on the MC56F8014 with PWM outputs fault inputs fault tolerant design with dead time insertion supporting both center aligned and edge aligned modes e 12 bit
53. ult Stopped gates tri stated Disabled Tri stated The following FreeMASTER software control actions are supported e Start the motor e Stop the motor e Set the required speed of the motor The FreeMASTER software displays the following information e Required speed of the motor e Actual speed of the motor e Application status INIT STOP RUN FAULT e DC bus voltage level e Motor current e Fault status overvoltage overcurrent undervoltage or Hall sensor cable error 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 40 Freescale Semiconductor Application Description Start the FreeMASTER software window s application bldc hall 56F8013 pmp Figure 6 1 illustrates the FreeMASTER software control window for the application running File Edit View Explorer tem Project Tools Help Pg DCDC invertor Designed By ey Launched by Motorola B Speed Pe P 488 Rising edge Roznov CSC Transportation amp Standard Product Group Roznov pod Radhostem Czech Republ Eaa fr eesca le 44 Falling edge semi miconductor 144 Both edges rising trigger iMac eee 3 ph BLDC Motor Control using Hall Sensors Cr controlled by DC DC Inverter 48 Main Scope 10 1 20 og 5 0 30 DE Bus Voltage V Mode Running DCDC voltage step 0 15 DCDC voltage step 3 8 D DCDC voltage step 4 6 D Speed step Required Speed Speed step 0 30k Requir T 5 Speed step 10k 15
54. via an RS232 serial cable A small program resident in the digital signal controller communicates with the FreeMASTER software to parse commands return status information to the PC and process control information from the PC FreeMASTER software executing on a PC uses part of Microsoft Internet Explorer as the user interface The FreeMASTER software is part of the Freescale Semiconductor Quick Start and may be selectively installed during the Quick Start installation The baud rate of the SCI communication for this application is 14400 baud It is set automatically by the FreeMASTER software driver and can be changed if necessary A detailed description of the FreeMASTER software is provided in the dedicated FreeMASTER for Embedded Applications documentation The 3 phase BLDC motor control application utilizes FreeMASTER software for remote control from the PC It enables the user to e Control starting and stopping e Set the motor speed 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 37 Software Design Variables read by the FreeMASTER software and displayed to the user are Required motor speed and actual motor speed Application operational mode Start stop status DC bus voltage variable DC link six step inverter output voltage motor current Overvoltage undervoltage overcurrent and Hall sensor cable faults Hall sensor state using the on line scope The Hall sensor state must be
55. vmin low 608 min position difference 60s min 237RPM 5 1 1 u max_period_low B 262 14ms 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 36 Freescale Semiconductor FreeMASTER Software 5 Now we can calculate the coefficient for the speed calculation Signed 16 bit fractional arithmetic is used so the maximum number can be 32767 The coefficients are then vmin 3662RPM mwwOMEGA ACTUAL MECH CONST 32767 eT 32767 38000RPM 3158 5 12 vmin_low 237RPM MEGA_ACTUAL_MECH NST LOW 32767 32767 mwwOMEGA_ACTU CH_CONS O 3276 una on 3276 A750RPM 1579 5 13 6 The speed is then calculated simply using the information of timer increments between two Hall sensor edges so mwwOMEGA ACTUAL MECH CONST mfwOmegaActualMech counted edges 5 14 However since the lower speed limit is set by the higher speed limit divided by 8 the lower speed result must be divided by 8 meaning shifted by 3 to the right mwwOMEGA_ACTUAL_MECH_CONST LOW counted edges mfwOmegaActualMech gt 3 5 15 7 Andthe speed in RPM is as follows 32767 corresponds to 38000 vmax so _ mfwOmegaActualMech speed_in_RPM 39767 vmax 5 1 6 5 5 FreeMASTER Software The FreeMASTER software was designed to provide an application debugging diagnostic and demonstration tool for the development of algorithms and applications It runs on a PC connected to the controller board
56. witchState 0 mfwOverCurrent lt TRESHOLD OVERCURRENT mwwOverVoltageCounter 0 mwwUnderVoltageCounter 0 mwwOverVoltageCounter gt FAULT COUNTER OVER VOLTAGE mfwOverCurrent gt TRESHOLD OVERCURRENT mwwUnderVoltageCounter gt FAULT COUNTER UNDER VOLTAGE STOPPED State muwwMissedCommutationsCount gt ko i FAULT COUNTER HALL SENSORSVOLTAGE mintSwitchState 0 mintSwitchState 1 Figure 5 4 Drive State Machine Transitions 3 Phase BLDC Drive Using Variable DC Link Six Step Inverter Rev 1 Freescale Semiconductor 33 Software Design 5 3 3 1 INIT State The INIT state initializes several state variables and sets up some peripherals e Turns off the MOSFET pre drivers by GPIO BO e Disables the MOSFET PWM signals by forcing them into tri state PWM 0 5 GPIO B2 B5 e Disables the brake resistance control pin and forces it into tri state GPIO B1 e Resets the required speed desired variable DC link six step inverter output voltage variable DC link six step inverter PI controller integral portion and fault occurrence variables e If the switch is turned off and no under or overvoltage or overcurrent condition is present the STOPPED state is entered 5 3 3 2 STOPPED State The application remains in this state as long as the switch is turned off If an undervoltage overvoltage or overcurrent fault is present the FAULT state is entered The MOSFET pre drivers are still turned off so no volta
57. y second PWM reload interrupt routine call meaning it is calculated at a frequency of 50kHz every 20us The measured and filtered variable DC link six step inverter output voltage is fed to the PI controller The difference between the desired voltage mfwDesiredDCDCVoltage and the measured voltage mfwDCDCVoltage is the error This controller s output is just the duty cycle for the variable DC link six step inverter MOSFETs mwwDuty Its absolute value is written either into PWM channel 4 or 5 If it is positive channel 4 is loaded with the duty cycle value and channel 5 is loaded with 0 vice versa if it is negative 5 2 3 Commutation On each new edge of the Hall sensor signals a capture interrupt phase A and or a GPIO interrupt phase B C is called The interrupt routine saves the actual Hall sensor state to muwwHallSensorsState The muwwHallSensorsState variable is input to the mask and swap calculation determining the final shape of the output voltage The output variable mudt PWMState is written directly to the PWM block channels 0 to 3 and GPIO A6 and B3 The next task performed by an interrupt routine is the calculation of the spin direction The result miwDirectionSpinning is used for the speed calculation For speeds greater than 500 RPM the system calculates the next Hall sensors commutation state in every commutation interrupt When the new commutation edge arrives the system compares it with this predicted state If the real Ha
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